Waterproofing, self environment-cleaning and other performance properties
ICT building construction admixtures are those ingredients in concrete other than Portland cement, water, and aggregates used to enhance the properties of the concrete.

Indoor Environmental Quality, or IEQ, refers to a suite of characteristics, such as indoor air quality, thermal comfort, daylighting and visual quality, and acoustics, that combine to make a building comfortable and optimally functional for the occupants. “Sick-building Syndrome” and mold have been in the news so indoor air quality is perhaps the most familiar aspect of IEQ. Poor air quality results from dust and other fine particulates, as well as emissions of volatile organic compounds (VOCs) which are chemicals used in paints, adhesives, carpet, and other common building materials. Particles and VOCs are irritants to many people, exacerbating conditions like allergies, asthma and chemical sensitivities. Most people now spend 75-90% of their time indoors, so the condition of the interior air can have a significant affect on their health. Other IEQ factors are linked to human performance. Studies with students and employees have shown that performance improves when they have access to good quality electric lighting, daylight, and views, appropriate levels of sound, and a comfortable, controllable, temperature. Post-occupancy studies by the Center for the Built Environment at UC Berkeley found that thermal comfort and acoustics evoked the most dissatisfaction by building occupants.

Why Does Concrete Help?

The properties of both concrete itself and concrete construction styles offer attributes to help make places that are comfortable for people to live and work.

Concrete can serve as both a structural and a finish material, reducing VOCs from additional finishes.

It is resistant to water damage.

It is an air and sound barrier.

When properly employed concrete’s thermal mass can offer greater thermal comfort, since radiant heating and cooling (the temperature of surfaces) can affect comfort as much as the air temperature.

It has the structural strength to allow maximum glazing to achieve daylight and view objectives through internal support columns and longer spans.

Indoor Air Quality

Building interior constructed of concrete masonry. (PCA No. 14510)

Because it can serve as both a structural and a finish material, concrete can reduce the need for additional finish materials. In addition to saving resources, this reduces the pathways for introducing VOCs into a space, since they often come from the finish materials themselves and the adhesives used to install them. The same concrete that is used as the floors and foundation slab can be polished and beautifully stained as a floor, with no need for resilient flooring adhesives or carpet. In addition, carpet is linked to higher levels of allergens because it holds dust and can harbor mites and mildew, so a finished concrete floor eliminates this as well. Exposed concrete walls do not require additional finish materials. When sealants are applied, it is important to look for ones with low VOCs and assure proper ventilation.

Concrete (3 in. or more in thickness) acts as an air barrier. This helps improve indoor air quality by limiting the amount of moisture than can enter a building or wall through infiltration. It also provides better control for the heating, ventilating and air-conditioning (HVAC) system.

Concrete does not contribute to indoor air quality problems caused by flooding. Concrete is not damaged by water; concrete that does not dry out continues to gain strength in the presence of moisture. Concrete submerged in water absorbs very small amounts of water over long periods of time. In flood-damaged areas, concrete buildings are often salvageable. Conversely, building materials such as wood and gypsum wallboard can absorb large quantities of water and cause moisture related problems.

Moisture problems may occur if concrete is enclosed in a system that traps moisture between the concrete and other building materials. For instance, vinyl wall coverings in hot and humid climates will act as a vapor retarder trapping moisture between the concrete and the wall covering. For this reason, impermeable wall coverings (vinyl wallpaper) should not be used on concrete walls. Likewise, a vapor barrier is required under a slab that will have a floor covering such as carpet or resilient flooring. The vapor barrier prevents water vapor in the ground from moving through the concrete into a building.

Construction waste related debris can be another source of indoor air pollution. A number of steps are recommended as part of a Construction IAQ Plan to help reduce this including blocking off ductwork, changing filters, keeping materials dry and airing out the space before occupancy. Concrete in general, and particularly precast concrete can help by reducing dust during construction. Using low-VOC form release agents and admixtures is another step to minimize the introduction of pollutants during construction.

Acoustic Comfort

Concrete walls provide a buffer between

Outdoor noise and the indoor environment in a building

Highway noise and neighborhoods with a sound barrier

Indoor noise between adjoining apartments or other spaces as a separating wall

Maryland State Highway 216 used decorative forms to create a sound barrier that is as artistic as it is effective (Photo courtesy of Creative Formliners)

The greater mass of concrete walls can reduce sound penetrating through a wall by over 80% compared with wood or steel frame construction. Although some sound will penetrate the windows, a concrete building can be two-thirds quieter than a wood or steel frame building. Concrete panels also provide effective sound barriers separating buildings from highways or industrial areas from residential areas.

Compared to a typical wood frame wall, only about one-quarter to one-eighth as much sound penetrates a concrete wall. Acoustics experts would describe loud speech on the opposite side of a frame wall as “audible, but not intelligible.” On the opposite side of a concrete wall, a listener would “strain to hear” loud speech. Through some concrete walls, loud speech would be “inaudible.”

A 2 x 4 wood stud partition wall with ½ in. gypsum wallboard on each side has a Sound Transmission Class (STC) of about 35. With the addition of furring, insulation, and wallboard, STC values up to 63 are obtained for 6 and 8 in. thick concrete walls. Bare concrete and masonry walls have STCs in the range of 45 to 50. Standard flat panel ICF walls generally have STCs in the range of 55 to 60. A subjective description of STC values is presented in the table.

STC -Lab

STC - Field

Subjective description of effectiveness

26-30

20-22

Most sentences clearly understood

30-35

25-27

Many phrases and some sentences understood without straining to hear

35-40

30-32

Individual words and occasional phrases clearly heard and understood

42-45

35-37

Medium loud speech clearly audible, occasional words understood

47-50

40-42

Loud speech audible, music easily heard

52-55

45-47

Loud speech audible by straining to hear; music normally can be heard and may be disturbing

57-60

50-52

Loud speech essentially inaudible; music can be heard faintly but bass notes disturbing

Surface temperatures can play as great a role in determining thermal comfort as air temperatures because of the effect of radiant heat. The temperature of walls and surfaces surrounding a person affect the amount of radiant heat transmitted to a person (from warm surfaces) or away from a person (to cold surfaces). Warm or cool ceilings, walls, and floors can cause discomfort of building occupants. Properly insulated concrete and masonry has thermal mass that will impart a more uniform temperature than other building materials. (Whether to insulate or not and how much depends on the climate).

Looking up towards the skylight at the St. Louis Priory Church and School, St. Louis, Mo. The concrete acts as the structural support and interior finish. The building is a parabola in cross-section, with the ribs converging at the skylight. (PCA No. 13713)

Concrete has negligible air infiltration. This reduces drafts that can cause discomfort, especially at floor level. This also reduces thermal stratification, or vertical temperature differences in a room. This generally occurs when a person’s head is more than 5°F warmer than their feet.

Daylight and views

Concrete floors can be designed to minimize beam depths and maximize daylight and views though windows. An interior concrete core can be designed to accommodate the majority of the structural load and shear forces, allowing for less obstructions along the perimeter of the building. Post tensioning can be used to obtain long floor spans, also minimizing the number of columns that obstruct views.

LEED Credits in IEQ

Concrete can contribute to LEED credits for Indoor Environmental Quality. The two most direct points it can help achieve are for low VOC coatings and carpet (Credit 4.2 and 4.3). LEED version 2.2 recognizes that alternatives that eliminate the need for additional finishes meet the intent of these credits, originally intended for paint, sealants, and carpet. Unfinished concrete walls, and concrete flooring that meets the standard (Carpet and Rug Institutes Green Label), may qualify.

The thermal mass properties of concrete can also help achieve IEQ Credit 7: Thermal Comfort. The use of concrete in and of itself does not qualify for a point, but it's ability to slow the building's reaction to temperature changes can shift the peak temperature to after the main period of occupancy in a commercial building for example. Additionally, thermal mass affects temperature perceived by the occupants through radiance rather than air temperature, radiant heating and cooling can be more comfortable that air flow.

Finally, concrete gives some design capabilities that can be used to faciliate daylighting strategies. Concrete can particularly help achieve a structure that allows more daylight deeper into a building. This may aid in achieving IEQ Credit 8.